Temporal coding for hearing implants

ABSTRACT

A system and method is provided for activating electrodes in a multi-channel electrode array having electrodes that are spatially divided. At least one pulse for stimulating a single electrode of the electrode array is determined. Each of the pulses is converted into a plurality of pulses for stimulating a plurality of electrodes in the electrode array.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional patentapplication Ser. No. 61/720,600 filed Oct. 31, 2012, entitled “TemporalCoding for Hearing Implants,” which is hereby incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to temporal coding for hearing implants,and more particularly to evaluation and methodology of temporal codingfor a cochlear implant.

BACKGROUND ART

A human ear normally transmits sounds such as speech sounds as shown inFIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102,which moves the bones of the middle ear 103 (malleus, incus, and stapes)that vibrate the oval window membrane of the cochlea 104. The cochlea104 is a long narrow duct wound spirally about its axis forapproximately two and three quarters turns. It includes three chambersalong its length: an upper chamber known as the scala vestibuli, amiddle chamber known as the scala media, and a lower chamber known asthe scala tympani. The cochlea 104 forms an upright spiraling cone witha center called the modiolus where the axons of the auditory nerve 113reside. These axons project in one direction to the cochlear nucleus inthe brainstem and they project in the other direction to the spiralganglion cells and neural processes peripheral to the cells (hereinaftercalled peripheral processes) in the cochlea. In response to receivedsounds transmitted by the middle ear 103, sensory hair cells in thecochlea 104 function as transducers to convert mechanical motion andenergy into electrical discharges in the auditory nerve 113. Thesedischarges are conveyed to the cochlear nucleus and patterns of inducedneural activity in the nucleus are then conveyed to other structures inthe brain for further auditory processing and perception.

Hearing is impaired when there are problems in the ability to transduceexternal sounds into meaningful action potentials along the neuralsubstrate of the cochlea 104. In some cases, hearing impairment can beaddressed by an auditory prosthesis system such as a cochlear implantthat electrically stimulates auditory nerve tissue with small currentsdelivered by multiple electrode contacts distributed along an implantelectrode. FIG. 1 shows some components of a typical cochlear implantsystem where an external microphone provides an audio signal input to anexternal signal processing stage 111 which implements one of variousknown signal processing schemes. The processed signal is converted bythe external signal processing stage 111 into a digital data format,such as a sequence of data frames, for transmission into a receiverprocessor in an implant housing 108. Besides extracting the audioinformation, the receiver processor in the implant housing 108 mayperform additional signal processing, and produces a stimulation pattern(based on the extracted audio information) that is sent through anelectrode lead 109 to an implanted electrode array 112 which penetratesinto the cochlea 104 through a surgical opening called a cochleostomy.Typically, this electrode array 112 includes multiple electrode contacts110 on its surface that deliver the stimulation signals to adjacentneural tissue of the cochlea 104 which the brain of the patientinterprets as sound. The individual electrode contacts 110 may beactivated using various stimulation strategies that include, forexample, sequential or simultaneous stimulation in one or more contactgroups.

The representation of temporal information in an auditory system by useof cochlea implants is imperfect compared to a normal functioninghearing organ. In a healthy ear, temporal information is recorded by thehair cells and their corresponding nerve fibers before the informationis translated to the brain. Up to a certain frequency, the hair cellscan follow the externally generated acoustic information in phase withthe corresponding oscillation of the basilar membrane. However, thenerve fibers have a certain refractory period which allows only alimited temporal coding. In case of a healthy physiological system,there are sufficient nerve fibers present having different refractorystates after stimulation. Consequently, acting as an ensemble, thesenerve fibers together are typically able to represent temporalinformation up to 5 kHz (see, for example, Wever and Bray's “volleytheory,” 1937).

In case of a cochlear implant, the temporal information is provided viathe electrodes by, for example, biphasic electrical pulses whichdirectly elicit action potentials in the nerve fibers. As a consequence,all nerve fibers around an electrical contact of the cochlear implantelectrode are elicited synchronously and the volley principal is notapplicable any more. Transfer of temporal information may thus bestrongly impaired.

The coupling to the neuronal system is therefore imperfect with regardto a cochlear implant. Further, conditions like the actual impedance ofthe cochlear implant's electrode contacts may be different from patientto patient. As a consequence, standardized pulse sequences may besub-optimal for patients. To help address this problem, psycho-acoustictests have been performed in which the patient provides subjectivefeedback whether he is able to discriminate pitch of presented sounds atvarious pulse rates. (See Bahmer and Baumann 2012, Cochlear ImplantsInternational, accepted). However, such subjection feedback can varydepending on the circumstances, and may be hard to achieve with certainpatients, for example, small children.

SUMMARY OF THE EMBODIMENTS

In accordance with an embodiment of the invention, a method is providedfor activating electrodes in a multi-channel electrode array havingelectrodes that are spatially divided. The method includes determiningat least one pulse for stimulating a single electrode of the electrodearray. Each of the pulses is converted into a plurality of pulses forstimulating a plurality of electrodes in the electrode array.

In accordance with related embodiments of the invention, converting mayinclude adding temporal separation between at least two pulsesassociated with different electrodes. The pulses for stimulating aplurality of electrodes may be at a supra-threshold pulse or asub-threshold pulse. The energy of the plurality of pulses may besubstantially equal to the energy of the pulse for stimulating the firstelectrode. The temporal and/or spatial center of mass for the pluralityof pulses may be substantially equivalent to that of the determinedpulse. The plurality of pulses may vary in amplitude, pulse length,and/or temporal separation. The variation may be based on a Gaussiandistribution, a Poisson distribution, and/or a uniform Distribution. Theat least one pulse for stimulating a single electrode of the electrodearray may be a plurality of pulses that form a sequential pulsesequence, such as a Continuous Interleaved Sampling (CIS) speech signalprocessing strategy.

In accordance with still further related embodiments of the invention,the method may further include stimulating the plurality of electrodesbased, at least in part, on the converted pulses. The electrode arraymay be part of an auditory prosthesis that is implanted in a user, themethod further including performing at least one neurophysiologicmeasurement upon stimulating the electrodes, and evaluating theneurophysiologic measurements so as to determine the quality of temporalcoding for enhanced pitch discrimination. The at least oneneurophysiologic measurement may include electrically evoked auditorysteady state responses (EASSR), electrically evoked brainstem responseaudiometry (EBERA), near field measurements, and/or electrically evokedcompound action potentials (ECAP). Evaluating the neurophysiologicmeasurements may include statistical testing and/or use of a geneticalgorithm. The pulse rate may be adjusted based on the evaluation. Themulti-channel electrode may be associated with an implant. Themulti-channel electrode array may be associated with a cochlear implant,a brain stem implant, or deep brain stimulation.

In accordance with another embodiment of the invention, an auditoryprosthesis system includes a stimulator adapted to be implantable, thestimulator including a plurality of electrodes forming a multi-channelelectrode array. A processor is configured to determine at least onepulse for stimulating a single electrode of the electrode array. Theprocessor is further configured to convert each of the pulses into aplurality of pulses for stimulating a plurality of electrodes in theelectrode array.

In accordance with related embodiments of the invention, the processormay be configured to add temporal separation between at least twoconverted pulses associated with different electrodes. The pulses forstimulating the plurality of electrodes may be a supra-threshold pulseor a sub-threshold pulse. The energy of the plurality of pulses may besubstantially equal to the energy of the determined pulse forstimulating the first electrode. The temporal and/or spatial center ofmass for the plurality of pulses may be substantially equivalent to thatof the determined pulse. The plurality of pulses may vary in amplitude,pulse length, and/or temporal separation. The variation may be based ona Gaussian distribution, a Poisson distribution, and/or a uniformDistribution. The at least one pulse for stimulating a single electrodeof the electrode array may be a plurality of pulses that form asequential pulse sequence. The sequential pulse sequence may be based ona Continuous Interleaved Sampling (CIS) speech signal processingstrategy.25. The stimulator may be configured to stimulate the pluralityof electrodes based, at least in part, on the converted pulses.

In accordance with still further embodiments of the invention, the testmodule may be configured to perform at least one neurophysiologicmeasurement on a user of the prosthesis to the electrode stimulation.The test module may be further configured to evaluate theneurophysiologic measurements so as to determine the quality of temporalcoding for enhanced pitch discrimination. Evaluating theneurophysiologic measurements may include statistical testing and/or useof a genetic algorithm. The neurophysiologic measurement may includeelectrically evoked auditory steady state responses (EASSR),electrically evoked brainstem response audiometry (EBERA), near fieldmeasurements, and/or electrically evoked compound action potentials(ECAP).

In accordance with another embodiment of the invention, a method ofevaluating the quality of temporal coding for enhanced pitchdiscrimination associated with a auditory prosthesis is provided. Theauditory prosthesis includes a plurality of electrodes in amulti-channel electrode array. The method includes stimulating theelectrodes at a pulse rate. At least one neurophysiologic measurement isperformed on a user of the prosthesis to the electrode stimulation. Theneurophysiologic measurements are evaluated so as to determine thequality of temporal coding for enhanced pitch discrimination. The pulsepattern and/or rate is adjusted based on the evaluation.

In accordance with related embodiments of the invention, theneurophysiologic measurement may include electrically evoked auditorysteady state responses (EASSR), electrically evoked brainstem responseaudiometry (EBERA), near field measurements, and/or electrically evokedcompound action potentials (ECAP). Evaluating the neurophysiologicmeasurements may include statistical testing and/or using a geneticalgorithm. Performing the at least one neurophysiologic measurement maybe done without subjective feedback from the user.

In accordance with another embodiment of the invention, an auditoryprosthesis system includes a plurality of electrodes in a multi-channelelectrode array. A stimulator is configured to stimulate the electrodesat a pulse rate. The system further includes means for performing atleast one neurophysiologic measurement on a user of the prosthesis tothe electrode stimulation, means for evaluating the neurophysiologicmeasurements so as to determine the quality of temporal coding forenhanced pitch discrimination; and means for adjusting the pulse patternand/or rate based on the evaluation.

In accordance with related embodiments of the invention, theneurophysiologic measurement may include electrically evoked auditorysteady state responses (EASSR), electrically evoked brainstem responseaudiometry (EBERA), near field measurements, and/or electrically evokedcompound action potentials (ECAP). The means for evaluating theneurophysiologic measurements may include statistical testing and/or useof a genetic algorithm. The means for performing the at least oneneurophysiologic measurement may be done without subjective feedbackfrom the user.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of embodiments will be more readily understood byreference to the following detailed description, taken with reference tothe accompanying drawings, in which:

FIG. 1 shows anatomical structures and system components in a human earhaving a cochlear implant system;

FIG. 2 shows a flow chart illustrating a method of activating electrodesin a multi-channel electrode array, in accordance with an embodiment ofthe invention;

FIG. 3 illustratively shows a single pulse on an electrode channel thathas been converted to a composite of three pulses on three electrodechannels, in accordance with an embodiment of the invention;

FIG. 4 shows a flow chart illustrating a method of evaluating thequality of temporal coding for enhanced pitch discrimination associatedwith an auditory prosthesis, in accordance with an embodiment of theinvention; and

FIG. 5 shows an EASSR evaluated by statistical testing, in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In illustrative embodiment of the invention, enhanced pulse stimulationsequences are identified that accurately represent temporal informationto hearing implant users. The modified pulse sequences may be patientspecific, such that they differ from user to user. In furtherembodiments of the invention, neurophysiologic measurements for ahearing implant are used as the basis for evaluating the quality oftemporal coding for enhanced pitch discrimination. The neurophysiologicmeasurements may be taken without, or used in combination with,subjective feedback from the user of the implant. Details are discussedbelow.

FIG. 2 shows a flow chart illustrating a method of activating electrodesin a multi-channel electrode array, in accordance with an embodiment ofthe invention. The multi-channel electrode array may be associated withan implant. The implant may be any implant known in the art thatincludes pulsed stimulation. For example, the multi-channel electrodearray may be associated with a hearing implant, such as a cochlearimplant, in which the electrodes of the electrode are positioned suchthat they are spatially divided within the cochlea. The cochlear implantmay be partially implanted, and include, without limitation, an externalspeech processor, microphone and/or coil, with an implanted stimulatorand/or electrode array. In other embodiments, the cochlear implant maybe a totally implanted cochlear implant. In further embodiments, themulti-channel electrode may be associated with deep brain stimulation(DBS) or a brainstem implant, such as an auditory brainstem implant.

At least one pulse is determined for stimulating a single electrode ofthe electrode array, step 201. In various embodiments, the implantemploys a stimulation strategy that provides pulsatile stimuli in amulti-channel electrode array. The at least one pulse may be, withoutlimitation, a plurality of pulses that form a sequential pulse sequencefor a given electrode. One specific example of a stimulation strategy isthe “Continuous Interleaved Sampling (CIS)”-strategy, as described byWilson et al., Better Speech Recognition With Cochlear Implants, Nature,vol. 352:236-238 (1991), which is incorporated herein by reference inits entirety. For CIS, symmetrical biphasic current pulses are used,which are strictly non-overlapping in time across the plurality ofelectrodes. The rate per channel typically is higher than 800pulses/sec. It is to be understood that the invention is not limited toCIS strategies, and is applicable with other stimulation strategiesknown in the art, such as, but not limited to, simultaneousactivation/overlapping of electrode currents. For example, and withoutlimitation, one such simultaneous stimulation is described in U.S. Pat.No. 6,594,525 (Zierhofer), which is incorporated herein by reference inits entirety.

Each of the pulses is converted into a plurality of pulses forstimulating a plurality of electrodes in the electrode array, step 203.For example, instead of presenting a pulse sequence comprising nindividual pulses on a single electrode channel (main channel), each ofthe n individual pulses associated with the pulse sequence may betransformed into a composite of pulses. Each of those composites ofpulses may comprise pulses distributed over several electrode channels(main and neighboring channels; spatial separation) and, in addition,temporal jitter between each pulses of the composite (temporalseparation) may be introduced. The pulses in the composite of pulses maybe supra- and/or subthreshold. Acting as an ensemble, the composite ofpulses advantageously allows enhanced representation/interpretation ofthe temporal information. Involving several channels instead of justone, the use of composite pulses leads to a spread of temporalinformation to a larger and more distributed number of nerve fibers,thus reducing the problem of eliciting the corresponding nerve fiberssynchronously.

FIG. 3 illustratively shows a single pulse on electrode channel E2 thathas been converted to a composite of three pulses on channels E1, E2 andE3, in accordance with an embodiment of the invention. Temporal jitterbetween the pulses on channels E1, E2 and E3 has been introduced. Thenumber of electrode channels upon which the composite of pulses isintroduced is not limited to three; any number of channels may beutilized. The composite of pulses may utilize, to varying degrees,sequential and/or simultaneous stimulation.

The energy of each pulse composite may be substantially equal to theenergy of the corresponding individual pulse out of the pulse sequence.Further, the center-of-mass of the composite pulses (spatial and/ortemporal) may be presented where the individual pulse would have beenpresented in order to preserve the tonotopic order.

Parameters of the composite pulses that may be varied include, withoutlimitation, amplitude distributions of the pulses within the pulsecomposites, the number of electrode channels used for the pulsecomposites, and pulse lengths of pulses within the pulse composites.Another parameter which may be varied is the temporal distributionsbetween the pulses within the pulse composites. The jitter/timedifferentiation between the composite pulses may be of any duration. Forexample, the time differentiation may be, without limitation, on theorder of μs or ms. The above-described distributions may be, withoutlimitation, according to a Gaussian distribution, Poisson distributionand/or uniform distribution. All of the above-described parameters mayalso be varied between corresponding pulses of subsequent pulsecomposites.

In various embodiments of the invention, the jitter/time differentiationbetween the composite pulses may be based on one or more rules.Illustratively, there may be a predefined minimum time differencebetween the composite pulses. The minimum time difference between thecomposite pulses may be determined by the intensity of the originalpulse (i.e., the corresponding individual pulse out of the pulsesequence). The minimum jitter/time differentiation may vary, so as tobe, without limitation, dependent on the levels between the compositepulses to avoid masking effects. For example, if the original pulse issplit into three pulses, the second of which has high intensity then thethird may be masked if it is presented at a neighboring channel unlessthere is sufficient time between these two pulses.

In accordance with even more sophisticated embodiments of the invention,the representation of a single pulse out of the composite of pulses(provided this single pulse is supra-threshold) may further berepresented by a sub-composite of pulses which includes sub- and/orsupra-threshold pulses, preferable sub-threshold pulses only. All thevariations of stimulation parameters explained above may be applied tothis sub-composite as well.

The rate of the n individual pulses of the pulse sequence which istransformed into a composite of pulses may be the basis for afrequency/rate analysis that may be used to evaluate the quality oftemporal coding for enhanced pitch discrimination. In variousembodiments, the jitter of the composite pulses is solely used forbetter representation of this rate.

FIG. 4 shows a flow chart illustrating a method of evaluating thequality of temporal coding for enhanced pitch discrimination associatedwith an auditory prosthesis, in accordance with an embodiment of theinvention. The auditory prosthesis may include a plurality of electrodesin a multi-channel electrode array, and utilize, without limitation, theabove-described pulse composite stimulation strategy; however otherstimulation strategies (including, for example, CIS and/or simultaneousstimulation strategies) are within the scope of the present invention.

The electrodes of the prosthesis are stimulated at a pulse rate, step401. At least one neurophysiologic measurement is then performed on auser of the prosthesis to the electrode stimulation, step 403. Invarious embodiments, the neurophysiological measurement may not requireany subjective user feedback.

The neurophysiological test may include electrically evoked auditorysteady state responses (EASSR) (see also: “Recording and online analysisof auditory steady state responses (ASSR) in Matlab”, Andreas Bahmer,Uwe Baumann; Journal of Neuroscience Methods 187 (2010), 105-113, whichis hereby incorporated herein by reference in its entirety; and“Temporal information transfer with cochlear implants: Improvements andMeasurements”, Habilitationsschrift, Andreas Bahmer, Frankfurt am Main,2012, which is hereby incorporated herein by reference in its entirety).EASSR responses to low-rate pulse trains can be readily recorded byelectrodes placed on the scalp of a cochlear implant user and separatedfrom the artifacts generated by the electrical stimulation.

In further embodiments, the neurophysiological test may includeelectrically evoked brainstem response audiometry (EBERA) or near fieldmeasurement methods like electrically evoked compound action potentials(ECAP). The various measurement methodologies may allow following theeffect of the composite pulses on temporal information transfer at adifferent levels of signal processing.

Referring back to FIG. 4, the neurophysiologic measurements areevaluated so as to determine the quality of temporal coding for enhancedpitch discrimination, step 405. The pulse pattern and/or rate may thenbe adjusted based on the evaluation, step 407, so as to provide optimalpitch discrimination for the user. Steps 405 and 407 may be repeateduntil a certain optimum is achieved (for example, convergence of agenetic algorithm).

The results of the neurophysiologic measurement may be evaluated bystatistical tests. Illustratively, and without limitation, the resultsof the neurophysiologic measurement (particularly EASSR) may beevaluated using the following two statistical test paradigms. Both allowsignal detection for a given significance threshold. A first testanalyzes and compares Fourier components of several subsequentmeasurements at the frequency of the signal modulation (see, forexample, “A new statistic for steady-state evoked potentials”, Victorand Mast, Electroencephalography and Clinical Neurophysiology, 1991,78:378-388, 1991, which is hereby incorporated herein by reference inits entirety). The second test evaluates Fourier components that areadjacent to the modulation frequency; these adjacent components are usedto estimate the noise level (see, for example: “Human auditorysteady-state responses to amplitude-modulated tones: phase and latencymeasurements” John and Picton, Hearing Research 141:57-79, 2000; and“MASTER: a Windows program for recording multiple”, John and Picton,Computer Methods and Programs in Biomedicine 61 125-150, 2000, each ofwhich is hereby incorporated herein by reference in its entirety). Inaddition, averaged data may be analyzed. Both test methods apply theF-test to estimate the probability that two subsets originate from thesame probability distribution.

In further embodiments, the result of the neurophysiologic measurement(particularly EABR) may be evaluated by the conformation of Jewett peaks(height and width). The result of the neurophysiologic measurement(particularly ECAP) may be evaluated by the conformation of P1-N1 peaks(height and width).

A genetic algorithm may use the evaluation results for rating thequality of temporal information transfer (so-called “cost-function”) forgeneration of a new set of parameters based on the previous sets ofparameter (see, for example, “Parameters for a model of an oscillatingneuronal network in the cochlear nucleus defined by genetic algorithms”,Andreas Bahmer, Gerald Langner; Bio. Cybernetics (2010), 102:81-93,which is hereby incorporated herein by reference in its entirety).

Illustratively, FIG. 5 shows an EASSR evaluated by statistical testing,in accordance with an embodiment of the invention (see, for example,FIG. 1 F-test example for ASSR from Bahmer and Baumann, 2010). Moreparticularly, FIG. 5 shows F Test probability when measuring ASSR with anormal hearing subject (x-axis: time [s], y-axis: test probability;headphone representation: sinusoidal amplitude modulated sine wave,carrier 1 kHz, modulation 97.656 Hz, 90 dB SPL). The F-test reachessignificance after approximately 75 s (the straight line indicatesalpha=0.05).

Embodiments of the invention may be implemented in whole or in part inany conventional computer programming language. For example, preferredembodiments may be implemented in a procedural programming language(e.g., “C”) or an object oriented programming language (e.g., “C++”,Python). Alternative embodiments of the invention may be implemented aspre-programmed hardware elements, other related components, or as acombination of hardware and software components.

Embodiments can be implemented in whole or in part as a computer programproduct for use with a computer system. Such implementation may includea series of computer instructions fixed either on a tangible medium,such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, orfixed disk) or transmittable to a computer system, via a modem or otherinterface device, such as a communications adapter connected to anetwork over a medium. The medium may be either a tangible medium (e.g.,optical or analog communications lines) or a medium implemented withwireless techniques (e.g., microwave, infrared or other transmissiontechniques). The series of computer instructions embodies all or part ofthe functionality previously described herein with respect to thesystem. Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Furthermore, suchinstructions may be stored in any memory device, such as semiconductor,magnetic, optical or other memory devices, and may be transmitted usingany communications technology, such as optical, infrared, microwave, orother transmission technologies. It is expected that such a computerprogram product may be distributed as a removable medium withaccompanying printed or electronic documentation (e.g., shrink wrappedsoftware), preloaded with a computer system (e.g., on system ROM orfixed disk), or distributed from a server or electronic bulletin boardover the network (e.g., the Internet or World Wide Web). Of course, someembodiments of the invention may be implemented as a combination of bothsoftware (e.g., a computer program product) and hardware. Still otherembodiments of the invention are implemented as entirely hardware, orentirely software (e.g., a computer program product).

Although various exemplary embodiments of the invention have beendisclosed, it should be apparent to those skilled in the art thatvarious changes and modifications can be made which will achieve some ofthe advantages of the invention without departing from the true scope ofthe invention.

What is claimed is:
 1. A method of activating electrodes in amulti-channel electrode array, in which the electrodes of themulti-channel electrode array are spatially divided, the methodcomprising: determining a pulse for stimulating a single electrode ofthe electrode array; converting the pulse into a plurality of pulses forstimulating a plurality of electrodes in the electrode array, whereinthe temporal and/or spatial center of mass for the plurality of pulsesis substantially equivalent to that of the determined pulse; andstimulating the plurality of electrodes based, at least in part, on theconverted pulses.
 2. The method according to claim 1, wherein convertingincludes adding temporal separation between at least two pulsesassociated with different electrodes.
 3. The method according to claim2, wherein the pulses for stimulating a plurality of electrodes is atleast one of a supra-threshold pulse and a sub-threshold pulse.
 4. Themethod according to claim 1, wherein the energy of the plurality ofpulses is substantially equal to the energy of the determined pulse forstimulating the single electrode.
 5. The method according to claim 1,wherein the plurality of pulses vary in amplitude, pulse length, and/ortemporal separation.
 6. The method according to claim 1, wherein thepulse for stimulating a single electrode of the electrode array is oneof a plurality of pulses that form a sequential pulse sequence forstimulating one or more electrodes in the electrode array.
 7. The methodaccording to claim 6, wherein the sequential pulse sequence is based ona Continuous Interleaved Sampling (CIS) speech signal processingstrategy.
 8. The method according to claim 6, further comprising, for atleast one or more electrodes in the multi-channel electrode arraydifferent from the single electrode, repeating the steps of determining,converting and stimulating.
 9. The method according to claim 8, whereinthe electrode array is part of an auditory prosthesis that is implantedin a user, further comprising: performing at least one neurophysiologicmeasurement upon stimulating the electrodes; evaluating theneurophysiologic measurements so as to determine the quality of temporalcoding for enhanced pitch discrimination.
 10. The method according toclaim 9, wherein the at least one neurophysiologic measurement includeselectrically evoked auditory steady state responses (EASSR),electrically evoked brainstem response audiometry (EBERA), near fieldmeasurements, and/or electrically evoked compound action potentials(ECAP).
 11. The method according to claim 1, wherein the multi-channelelectrode is associated with an implant.
 12. A method of activatingelectrodes in a multi-channel electrode array, in which the electrodesof the multi-channel electrode array are spatially divided, the methodcomprising: determining a pulse for stimulating a single electrode ofthe electrode array; converting the pulse into a plurality of pulses forstimulating a plurality of electrodes in the electrode array, whereinthe plurality of pulses vary in amplitude, pulse length, and/or temporalseparation, and wherein the variation is based on a Gaussiandistribution, a Poisson distribution, and/or a uniform Distribution; andstimulating the plurality of electrodes based, at least in part, on theconverted pulses.
 13. The method according to claim 12, whereinconverting includes adding temporal separation between at least twopulses associated with different electrodes.
 14. The method according toclaim 13, wherein the pulses for stimulating a plurality of electrodesis at least one of a supra-threshold pulse and a sub-threshold pulse.15. The method according to claim 12, wherein the energy of theplurality of pulses is substantially equal to the energy of thedetermined pulse for stimulating the single electrode.
 16. The methodaccording to claim 12, wherein the pulse for stimulating a singleelectrode of the electrode array is one of a plurality of pulses thatform a sequential pulse sequence for stimulating one or more electrodesin the electrode array.
 17. The method according to claim 16, whereinthe sequential pulse sequence is based on a Continuous InterleavedSampling (CIS) speech signal processing strategy.
 18. The methodaccording to claim 12, further comprising, for at least one or moreelectrodes in the multi-channel electrode array different from thesingle electrode, repeating the steps of determining, converting, andstimulating.
 19. The method according to claim 18, wherein the electrodearray is part of an auditory prosthesis that is implanted in a user,further comprising: performing at least one neurophysiologic measurementupon stimulating the electrodes; evaluating the neurophysiologicmeasurements so as to determine the quality of temporal coding forenhanced pitch discrimination.
 20. The method according to claim 19,wherein the at least one neurophysiologic measurement includeselectrically evoked auditory steady state responses (EASSR),electrically evoked brainstem response audiometry (EBERA), near fieldmeasurements, and/or electrically evoked compound action potentials(ECAP).
 21. The method according to claim 12, wherein the multi-channelelectrode is associated with an implant.
 22. A method of activatingelectrodes in a multi-channel electrode array that is part of anauditory prosthesis that is implanted in a user, in which the electrodesof the multi-channel electrode array are spatially divided, the methodcomprising: determining a pulse for stimulating a single electrode ofthe electrode array wherein the pulse for stimulating a single electrodeof the electrode array is one of a plurality of pulses that form asequential pulse sequence for stimulating one or more electrodes in theelectrode array; converting the pulse into a plurality of pulses forstimulating a plurality of electrodes in the electrode array;stimulating electrodes in the multi-channel electrode array based, atleast in part, on the converted pulses and the sequential pulsesequence; performing at least one neurophysiologic measurement uponstimulating the electrodes; and evaluating the neurophysiologicmeasurements so as to determine the quality of temporal coding forenhanced pitch discrimination, wherein evaluating the neurophysiologicmeasurements includes statistical testing.
 23. The method according toclaim 22, wherein evaluating the neurophysiologic measurements includesusing a genetic algorithm.
 24. The method according to claim 22, whereinconverting includes adding temporal separation between at least twopulses associated with different electrodes.
 25. The method according toclaim 24, wherein the pulses for stimulating a plurality of electrodesis at least one of a supra-threshold pulse and a sub-threshold pulse.26. The method according to claim 22, wherein the energy of theplurality of pulses is substantially equal to the energy of thedetermined pulse for stimulating the single electrode.
 27. The methodaccording to claim 22, wherein the plurality of pulses vary inamplitude, pulse length, and/or temporal separation.
 28. The methodaccording to claim 27, wherein the variation is based on a Gaussiandistribution, a Poisson distribution, and/or a uniform Distribution. 29.The method according to claim 22, wherein the sequential pulse sequenceis based on a Continuous Interleaved Sampling (CIS) speech signalprocessing strategy.
 30. The method according to claim 22, wherein theat least one neurophysiologic measurement includes electrically evokedauditory steady state responses (EASSR), electrically evoked brainstemresponse audiometry (EBERA), near field measurements, and/orelectrically evoked compound action potentials (ECAP).
 31. The methodaccording to claim 22, wherein the sequential pulse sequence has a pulserate, the method further comprising adjusting the pulse rate based onthe evaluation.
 32. The method according to claim 22, furthercomprising, for at least one or more electrodes in the multi-channelelectrode array different from the single electrode, repeating the stepsof determining and converting, and wherein stimulating further includesstimulation based, at least in part, on converted pulses associated withthe at least one or more electrodes in the multi-channel electrode arraydifferent from the single electrode.
 33. A method of activatingelectrodes in a multi-channel electrode array that is part of anauditory prosthesis that is implanted in a user, in which the electrodesof the multi-channel electrode array are spatially divided and in whichthe electrodes are stimulated at a pulse rate, the method comprising:determining a pulse for stimulating a single electrode of the electrodearray wherein the pulse for stimulating a single electrode of theelectrode array is one of a plurality of pulses that form a sequentialpulse sequence for stimulating one or more electrodes in the electrodearray, the sequential pulse sequence having a pulse rate; converting thepulse into a plurality of pulses for stimulating a plurality ofelectrodes in the electrode array; stimulating electrodes in themulti-channel electrode array based, at least in part, on the convertedpulses and the sequential pulse sequence; performing at least oneneurophysiologic measurement upon stimulating the electrodes; evaluatingthe neurophysiologic measurements so as to determine the quality oftemporal coding for enhanced pitch discrimination; and adjusting thepulse rate based on the evaluation.
 34. The method according to claim 33wherein converting includes adding temporal separation between at leasttwo pulses associated with different electrodes.
 35. The methodaccording to claim 34, wherein the pulses for stimulating a plurality ofelectrodes is at least one of a supra-threshold pulse and asub-threshold pulse.
 36. The method according to claim 33, wherein theenergy of the plurality of pulses is substantially equal to the energyof the determined pulse for stimulating the single electrode.
 37. Themethod according to claim 33, wherein the plurality of pulses vary inamplitude, pulse length, and/or temporal separation.
 38. The methodaccording to claim 37, wherein the variation is based on a Gaussiandistribution, a Poisson distribution, and/or a uniform Distribution. 39.The method according to claim 33, further comprising, for at least oneor more electrodes in the multi-channel electrode array different fromthe single electrode, repeating the steps of determining and converting,and wherein stimulating further includes stimulation based, at least inpart, on converted pulses associated with the at least one or moreelectrodes in the multi-channel electrode array different from thesingle electrode.
 40. The method according to claim 33, wherein thesequential pulse sequence is based on a Continuous Interleaved Sampling(CIS) speech signal processing strategy.
 41. The method according toclaim 33, wherein the at least one neurophysiologic measurement includeselectrically evoked auditory steady state responses (EASSR),electrically evoked brainstem response audiometry (EBERA), near fieldmeasurements, and/or electrically evoked compound action potentials(ECAP).
 42. The method according to claim 33, wherein evaluating theneurophysiologic measurements includes using a genetic algorithm.
 43. Anauditory prosthesis system comprising: a stimulator adapted to beimplantable, the stimulator including a plurality of electrodes forminga multi-channel electrode array; and a processor configured to:determine at least one pulse for stimulating a single electrode of theelectrode array; and convert each of the pulses into a plurality ofpulses for stimulating a plurality of electrodes in the electrode array;and a test module configured to perform at least one neurophysiologicmeasurement on a user of the prosthesis to the electrode stimulation,the test module further configured to evaluate the neurophysiologicmeasurements so as to determine the quality of temporal coding forenhanced pitch discrimination.
 44. The system according to claim 43,wherein the processor is configured to add temporal separation betweenat least two converted pulses associated with different electrodes. 45.A method of evaluating the quality of temporal coding for enhanced pitchdiscrimination associated with a auditory prosthesis, the auditoryprosthesis including a plurality of electrodes in a multi-channelelectrode array, the method including: stimulating the electrodes at apulse rate; performing at least one neurophysiologic measurement on auser of the prosthesis to the electrode stimulation; evaluating theneurophysiologic measurements so as to determine the quality of temporalcoding for enhanced pitch discrimination; and adjusting the pulsepattern and/or rate based on the evaluation.
 46. The method according toclaim 45, wherein performing the at least one neurophysiologicmeasurement is done without subjective feedback from the user.
 47. Themethod according to claim 45, wherein the at least one neurophysiologicmeasurement includes electrically evoked auditory steady state responses(EASSR), electrically evoked brainstem response audiometry (EBERA), nearfield measurements, and/or electrically evoked compound actionpotentials (ECAP).
 48. The method according to claim 45, whereinevaluating the neurophysiologic measurements includes statisticaltesting or a genetic algorithm, or both.
 49. An auditory prosthesissystem comprising: a plurality of electrodes in a multi-channelelectrode array: a stimulator for stimulating the electrodes at a pulserate; means for performing at least one neurophysiologic measurement ona user of the prosthesis to the electrode stimulation; means forevaluating the neurophysiologic measurements so as to determine thequality of temporal coding for enhanced pitch discrimination; and meansfor adjusting the pulse pattern and/or rate based on the evaluation. 50.The system according to claim 49, wherein the means for performing theat least one neurophysiologic measurement is done without subjectivefeedback from the user.